Interpretive Summary: Infection with the protozoan parasite Toxoplasma gondii is widespread in livestock and humans in the U.S. The ingestion of pork infected with Toxoplasma parasites is considered to be one of the main sources of infection. In order to develop control strategies to reduce or eliminate T. gondii in the nation's swine herds, it is imperative to obtain information on the reservoirs of infection and the modes of transmission of T. gondii to swine. Scientists at the Beltsville Agricultural Research Center and the University of Illinois have assessed risk factors for Toxoplasma infection in swine on 170 farms in Illinois. The access of Toxoplasma infected cats to swine barns and the presence of infected house mice were the two main risk factors associated with toxoplasmosis in swine. This information will be useful to pig producers, to veterinarians and public health specialists.

Technical Abstract:
Two epidemiologic studies (A and B) of risk factors for transmission of Toxoplasma gondii to swine were conducted on farms in Illinois. In study A there were 123 farms surveyed which provided blood samples for at least 30 sows. The mean seroprevalence of antibodies to T. gondii in sows was 19.5% (median = 10.0%). Multiple regression analysis of the association of seroprevalence with outdoor housing of sows, cat access to sow areas, number of sows, open feed storage and water delivery, delayed removal of carcasses, and presence of rodents on the farm indicated that higher seroprevalence was associated with cat access to sows (p= 0.009) and fewer sows in the herd (p= 0.05). Study B was a field investigation of 47 swine farms. Data collection included obtaining blood samples from swine, cats and rodents, and fecal samples from cats, heart and brain tissue from rodents, and feed, water, and soil samples for T. gondii examination. The risk of T. gondii transmission from cats and rodents to sows and finishing pigs was evaluated. Multiple regression analysis indicated that T. gondii seroprevalence in finishing pigs increased with more seropositive juvenile cats on the farm (p less than or equal to 0.0001), and higher seroprevalence in house mice (p= 0.0023). For sows, the only risk factor associated with increased T. gondii seroprevalence was a higher number of seropositive juvenile cats on the farm (p= 0.0008).